This story is part of MassLive's ongoing coverage of the Michelle Carter trial, potentially a landmark case in which a teenager is being charged with manslaughter for encouraging her boyfriend to kill himself.

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It was a friendship driven by a flood of text messages and centered, in part, around mental health, between two young women who struggled with eating disorders.

In the fall of 2014, that intimacy turned into evidence, when Michelle Carter texted Samantha Boardman that it was "her fault" her boyfriend Conrad Roy had killed himself that summer.

"I should have did more and it's all my fault because I could of stopped him but I f------ didn't," Carter wrote to Boardman on Sept. 15, 2014.

Boardman, a former classmate of Carter's at King Philip Regional High School, exchanged text messages with Carter after Roy's death in which Carter said she told Roy to get back in his truck when he became "scared" about killing himself.

Carter was a 17-year-old high school student when prosecutors say she pressured Roy into suicide and helped him research the techniques that allowed him to flood the cabin of his pickup truck with carbon monoxide in July of 2014.

Text messages between Roy and Carter show her repeatedly encouraging him to end his life, saying it would be "painless" and that it was his best option. Prosecutors have alleged she convinced him to follow through in a phone call on the day of his death, urging him to return to the car.

Carter's defense team has maintained that she committed no crime, and that Roy, who had a history of depression and a previous suicide attempt, was the architect of the plan to kill himself. The text messages are protected free speech and prosecutors have overreached by charging her with manslaughter, her attorneys have argued.

Boardman became friends with Carter in the spring of 2014, when they were in the same math class, she said Wednesday.

Their text conversations, which were extensive, often focused on eating disorders. Carter would text Boardman about what she had eaten, and Boardman would provide advice and check on her during school.

It was in some ways a mutual support system; Boardman also struggled with eating, she testified. But Carter needed constant support and assurance, both with her mental health and her social isolation. Carter frequently sent lengthy text messages and was aware she came on strong in her friendship, according to texts displayed in court.

"I don't know why people don't like me or wanna hang out like I don't get it," Carter wrote to Boardman. "Is something wrong with me that I can't see?"

On July 10, the night after Boardman attended a sleepover at Carter's home, Carter texted Boardman saying that Roy was missing.

"He's missing like they don't know where his is," she wrote.

Boardman expressed concern and they continued to talk about the situation. Carter -- who other text messages show had engaged in detailed discussions with Roy about his plans to kill himself with carbon monoxide -- acted as though she was unfamiliar with that suicide method.

"Is there any way a portable generator can kill you somehow?" Carter texted at 5:30 p.m., saying she had seen such a generator in Roy's possession.

The commonwealth argues that, beyond text messages pressuring Roy into suicide, Carter spoke with him on the phone as his truck cabin filled with carbon monoxide -- and urged him to follow through, despite his fears and second thoughts.

There is no recording of those two phone calls. But Carter texted Boardman after Roy's death and appeared to take responsibility for the suicide, the commonwealth has argued in court filings.

On the night of Roy's death, Carter texted Boardman saying she believed Roy was dead and calling herself "stupid" for overlooking the generator as a means of suicide.

"He just called me and there was a loud noise like a motor and I heard moaning," she wrote.

"I think he just killed himself," she continued.

On July 20, Carter told Boardman of her fears of being prosecuted when she learned police were searching Roy's phone, according to text messages displayed in the courtroom.

"Sam, [the police] read my messages with him I'm done," Carter wrote. "His family will hate me and I can go to jail."

Later, in September, Carter sent Boardman a lengthy text that largely focused on Roy's family and her efforts to help Roy's mother cope with his death.

But at the end of that text, Carter gave an account of Roy's death starkly different from what she had previously told friends -- one that said she told him to follow through with his suicide.

"Sam, [the victim's] death is my fault like honestly I could have stopped him I was on the phone with him and he got out of the [truck] because it was working and he got scared and I f------ told him to get back in Sam because I knew he would do it all over again the next day and I couldnt have him live the way he was living anymore I couldnt do it I wouldnt let him," Carter wrote.

Assistant District Attorney Maryclare Flynn quoted that text -- specifically Carter's claim that she "f------ told him to get back in" -- multiple times during her opening statement yesterday.